The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A power supply system may include one or more transfer switches to switch a load between a primary power source and a backup power source. For example, loads, such as hospitals, refrigeration systems, cell towers, and data centers require a consistent and reliable supply of electrical power. The load receives the electrical power from an electrical grid that delivers electricity from suppliers to consumers. Power from the electrical grid may be interrupted due to, for example, inclement weather, unforeseen accidents, and/or maintenance. Accordingly, a backup power supply, such as a generator, is used to maintain power to the load with as little interruption as possible. One or more uninterruptible power supply (UPS) devices may be used to power some or all of the load until the backup power supply is on-line.
In FIG. 1, a functional block diagram of an example power supply system is presented. The power supply system includes an automatic transfer switch 102 and a bypass transfer switch 106 (collectively referred to as transfer switches 102, 106). The transfer switches 102, 106 are operable to electrically connect to a primary power source 110 and a backup power source 114 (collectively referenced as power sources 110, 114). The transfer switches 102, 106 switch a load 118 between the primary power source 110 and the backup power source 114 such that the load 118 receives power from one of the power sources 110, 114.
The automatic transfer switch 102 includes an automatic switch control module 122 for monitoring and switching between the primary power source 110 and the backup power source 114. Specifically, the automatic transfer switch 102 may automatically switch from the primary power source 110 to the backup power source 114 in response to a voltage output by the primary power source 110 decreasing below an expected operating range. The automatic transfer switch 102 may automatically switch back to the primary power source 110 from the backup power source 114 in response to the voltage output by the primary power source 110 returning to the expected operating range.
The bypass transfer switch 106 is disposed in parallel with the automatic transfer switch 102, and can be a non-automatic transfer switch operable by an operator. The bypass transfer switch 106 can act as a backup to the automatic transfer switch 102 when the automatic transfer switch 102 is off-line. In particular, in the event that the automatic transfer switch 102 is taken off-line for, as an example, maintenance, the bypass transfer switch 106 is used to control the electrical power being supplied to the load 118.
The automatic transfer switch 102 includes a series of relays that connect the load 118 to each of the power sources 110, 114. The automatic switch control module 122 actuates the appropriate relay for electrically connecting the load 118 to one of the power sources 110, 114. It is important that the automatic transfer switch 102 not connect both of the two power sources 110, 114 to the load 118 at the same time. Such a simultaneous connection shorts the primary power source 110 and the backup power source 114 together, an undesirable situation that may cause damage to the load 118, the automatic transfer switch 102, and other components associated with the two power sources 110, 114.